Hard-to-weld (HTW) alloys, such as nickel-based superalloys and certain aluminum-titanium alloys, due to their gamma prime and various geometric constraints, are susceptible to gamma prime strain aging, liquation and hot cracking. These materials are also difficult to join when the gamma prime phase is present in volume fractions greater than about 30%, which may occur when aluminum or titanium content exceeds about 3%. As used herein, an “HTW alloy” is an alloy which exhibits liquation, hot and strain-age cracking, and which is therefore impractical to weld.
These HTW alloys may be incorporated into components of gas turbine engines such as airfoils, blades, shrouded blades, nozzles, shrouds, contact pads applied to inter-shroud contact surfaces of shrouded turbine blades, combustors, rotating turbine components, wheels, seals, 3d-manufactured components with HTW alloys and other hot gas path components. As used herein, “blade” is synonymous with “bucket”, and “vane” is synonymous with “nozzle”. Incorporation of these HTW alloys may be desirable due to often superior operational properties, particularly for certain components subjected to the most extreme conditions and stresses.
Shrouded blades are often made of nickel-based superalloys or other high temperature superalloys designed to retain high strength at high temperature. The material of the blade shrouds and the interlocking notch may lack sufficient hardness to withstand wear stresses and rubbing which occur during start-up and shut-down of a turbine engine, as the shrouded blades twist to an “interlocked” and “non-interlocked” position, respectively. Due to the relatively low Rockwell hardness of the typical materials of the blade shrouds and the interlocking notch, the interlocks may wear, resulting in gaps opening between the blade shrouds, thereby allowing the airfoils to twist and further deform, and even to possibly vibrate during operation which is highly undesirable as such imparts additional higher stresses on the blades which can quickly lead to blade breakage and consequent failure of the turbine. Contact pads may be applied to the inter-shroud contact surfaces of the interlocking notches to restore the interlocking capability of worn interlocking notches. However, desirable welding techniques such as gas tungsten arc welding, shielded metal arc welding, plasma arc welding, laser beam welding, and electron beam welding, are impractical to use to join contact pads to the inter-shroud contact surfaces where either or both of the contact pads and the inter-shroud contact surfaces incorporate HTW alloys.